GFP: Green fluorescent protein a versatile gene marker for entomopathogenic nematodes

Gene expression and protein distribution within cells may be monitored using reporters, such as, β-galactosidase, firefly luciferase, and bacterial luciferase. These reporter systems require exogenously added substrates and cofactors which kill the cells or organism. The jellyfish (Aequorea victoria) green fluorescent protein (gfp) gene has been used as a marker for gene expression in Caenorhabditis elegans. Because exogenous substrates or cofactors are not required for the fluorescence, gfp can be used to monitor gene expression in living organisms. Natural autofluorescence in nematodes however, can, hinder the use of such markers. We studied autofluorescence in entomopathogenic nematodes to explore the use of gfp as a marker for gene expression. All stages of Heterorhabditis and Steinernema spp. autofluorescent ranged from green to light yellow, the intensity of autofluorescence increased with the age of nematodes. We used gfp that was under the control of mec-4 promoter from C. elegans and injected the plasmid (pGFP/mec-4) into the gonad of Heterorhabditis bacteriophora using microinjection. Gfp was expressed in H. bacteriophora and was easily identified in the tail region of the nematode. Expression of mec-4 indicates the presence of touch receptors neurons in H. bacteriophora at the same position as in C. elegans. We conclude that gfp is an efficient marker for gene expression in entomopathogenic nematodes.